# Important Questions and Answers: Chemical Kinetics

1. Give a chemical reaction to show the reaction of first order.

Ans: The chemical reaction whose order is one is called first order reaction.

Consider a reaction,

NH4NO2 → N2 + 2H2O

Here, rate = K [NH4NO2]1

∴ Order of reaction = 1

2. What is activation energy?

Ans: The minimum amount of energy required to activate the proceed the chemical reaction is called activation energy. Mathematically, it can be related as:

∴ Activation energy (Ea) = Thrasehold energy (ET) – Average energy of reacting molecules (ER)

3. Define half life of the reaction.

Ans: The time required to decrease half of initial concentration of reactant is called half life of the reaction. It is denoted by t1/2. It is related to rate constant as:

It is related to rate constant as:
t1/2 = 0.693/k for first order reaction

4. What do you mean by rate of chemical reaction?

Ans: The rate of reaction can be defined as the decrease in concentration of reactants or increase in concentration of product per unit time.
Let us consider a general reaction A giving product.
i.e., $${\text{A} \rightarrow \text{Product}}$$
In time Δt, the rate of reaction is given by:
$$\text{Rate} = -\frac{{\delta}\text{A}}{{\delta}\text{t}}$$ = +\frac{{\delta}\text{B}}{{\delta}\text{t}}$$Here, -ve sign shows that the concentration of A decreases with time and +ve sign shows that the concentration of B increases with time. 5. What are the factors affecting rate of reaction? Ans: The different factors that affect the rate of reaction are given below. a. Temperature b. Concentration of reactants c. Catalyst d. Surface area of the reactants 6. Give an example of reaction where order and molecularity are equal. Ans: In reaction between hydrogen and iodine to give hydrogen iodide, both molecularity and order are same: H2 + I2 → 2HI The reaction is bimolecular and follows 2nd order kinetics. 7. How does a catalyst increases the rate of reaction? Ans: Catalyst increases the rate of reaction by decreasing the activation energy by providing alternate path to the reacting species. This can be shown by the energy profile diagram as shown below. 8. Write the possible rate law equations of the following second order reactions. P + Q → Product Ans: The possible rate law expressions for the following second order reaction can be given as: Rate = [P]1[Q]1 or, Rate = K[P]2[Q]0 or, Rate = K[P]0[Q]2 9. What is the order of reaction whose rate constant has the same unit as the rate of reaction? Ans: For a zero order reaction, the rate constant has same value as the rate of reaction. Consider a reaction A → Product If the reaction is of zero order then, rate = K[A]0 Here, K is the rate constant.$$or, -\frac{d[A]}{dt} = k or, \frac{molL^{-1}}{s} = kor, k = molL^{-1}s^{-1}$$So, k has the same unit as rate of the reaction. 10. What is effective collision? Ans: The collision that can form the desired product is called effective collision. The intermolecular collision of reactants gives effective collision. 11. Equal masses of finely divided metal catalyst is more efficient that the block of same metal. Why? Ans: A finely divided metal has larger surface area than the block of same weight. As the rate of reaction is directly proportional to surface area of the reactant, so equal mass of finely divided metal catalyst is more efficient that the block of same metal. 12. What is instantaneous rate of reaction? Ans: The rate of a reaction at any particular instant is called instantaneous rate of reaction.$$\text{i.e., Rate} = \frac{\text{dx}}{\text{dt}}
Where dt is the small interval of time and dx is the change in concentration at time interval dt.

13. Differentiate between order and molecularity of a reaction.

 Order of reaction Molecularity of reaction It is defined as the sum of concentration of reactants expressed in rate law. It is defined as the number of molecules which simultaneously collide to give new product. It is determined experimentally but cannot be calculated. It is a theoretical concept and and can be calculated. It may have fractional or zero value. It is always whole number. It changes with temperature, pressure, concentration etc. It is invariable with conditions.

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#### 7 Responses to “Important Questions and Answers: Chemical Kinetics”

1. Emanuel peter

2. johnmwanza98

these are interesting questions….more are needed

• john mwanza

these are interesting questions….more are needed

• Poonam

Yes

3. kazi sayef

Order is experimental value. Explain the line

4. Poonam

Significance of integrate first order and zero order is n’t given

5. Suman Prakash